langgraphjs/internal/build

LangChain Build System

A modern build system for LangChain JavaScript/TypeScript packages that provides fast compilation, type checking, automated secret management, and advanced code generation for monorepo workspaces.

Overview

This build system is designed to handle the complex requirements of LangChain's multi-package monorepo. It automatically discovers packages in the workspace, compiles them with optimal settings, and includes specialized tooling for LangChain's security patterns and dynamic loading capabilities.

Key Features

• 🚀 Fast Compilation: Uses tsdown for high-performance TypeScript bundling with Rolldown
• 📦 Monorepo Aware: Automatically discovers and builds all non-private packages in pnpm workspaces
• 🔍 Secret Management: Built-in scanning and validation of LangChain's lc_secrets patterns
• 📝 Type Generation: Generates both ESM and CommonJS outputs with TypeScript declarations
• ✅ Quality Checks: Integrated type checking with arethetypeswrong, publint, and unused dependency detection
• 🗺️ Import Maps: Automatic generation of import maps for convenient bulk imports
• 📋 Import Constants: Dynamic detection and export of optional dependency entrypoints
• 🎯 Selective Building: Build all packages or target specific ones with flexible filtering
• 👀 Watch Mode: Real-time compilation with file watching capabilities
• 🛠️ Rich CLI: Full-featured command-line interface with comprehensive options

Architecture

The build system consists of:

infra/build/
├── index.ts              # Main build orchestrator
├── cli.ts                # Command-line interface
├── types.ts              # TypeScript type definitions
├── utils.ts              # Utility functions
├── plugins/
│   ├── README.md         # Plugin documentation
│   ├── lc-secrets.ts     # LangChain secrets scanning plugin
│   ├── import-map.ts     # Import map generation plugin
│   └── import-constants.ts # Import constants generation plugin
├── package.json          # Build system dependencies
└── README.md             # This documentation

Core Technologies

• tsdown - Fast TypeScript bundler with Rolldown
• TypeScript Compiler API - For source code analysis and type checking
• unplugin-unused - For unused dependency detection
• Node.js built-ins - File system operations and process management

Usage

CLI Commands

# Get help
pnpm build:new --help

# Build all packages in the workspace
pnpm build:new

# Build with watch mode for development
pnpm build:new --watch

# Build specific packages
pnpm build:new @langchain/core
pnpm build:new @langchain/core langchain @langchain/openai

# Exclude packages from build
pnpm build:new --exclude @langchain/community
pnpm build:new -e @langchain/aws -e @langchain/openai

# Skip various build steps
pnpm build:new --no-emit          # Skip type declarations
pnpm build:new --skip-unused      # Skip unused dependency check
pnpm build:new --skip-clean       # Skip cleaning build directory
pnpm build:new --skip-sourcemap   # Skip sourcemap generation

Development

Adding New Packages

1. Create package directory under appropriate workspace
2. Add package.json with proper exports field
3. Add tsconfig.json extending workspace config
4. Run build - it will be automatically discovered

package.json Requirements

Each package must have a properly configured exports field that includes an input property to tell the build system which source file to compile for each entrypoint:

{
  "name": "@langchain/example",
  "exports": {
    ".": {
      "input": "./src/index.ts", // ← Required: Source file for this entrypoint
      "import": "./dist/index.js",
      "require": "./dist/index.cjs",
      "types": "./dist/index.d.ts"
    },
    "./tools": {
      "input": "./src/tools/index.ts", // ← Required: Source file for tools entrypoint
      "import": "./dist/tools/index.js",
      "require": "./dist/tools/index.cjs",
      "types": "./dist/tools/index.d.ts"
    }
  }
}

Important: The input property is required for the build system to understand which TypeScript source file should be compiled for each export. Without this property, the entrypoint will be ignored during build.